Selena Gomez had one of the toughest shows of her career this past weekend in Miami.

It had nothing to do with vocal or technical glitches. It was all about her grief over her friend Christina Grimmie, who was shot and killed at a concert in Orlando, Florida, last week.

Selena first broke down while singing 'Nobody' at the American Airlines Arena. She then sat down at the piano to dedicate the song 'Transfiguration' to 22-year-old Christina and completely lost it before singing a note.

"When she was 14, we met her – my parents and I signed her," Selena said. "And one thing about Christina and her family, is that she holds her faith so closely to her.

"It's not about her religion, and it's not about good deeds. It's just that she had faith. And I don't really understand how this happened, but I would like to dedicate this next song to her."

Christina and Selena onstage in Boca Raton, Florida, in 2011

Christina, who finished third in the sixth season of The Voice US in 2014, was shot on June 10 while signing autographs after a concert in Orlando. She died later that night.

Selena had been friends with Christina since their teens. Her stepfather, Brian Teefey, became Christina's manager after discovering her on YouTube.

Before her Miami show, Christina had tweeted about her friend to her 43.2 million followers.

She also shared a message from her stepfather Brian, announcing the creation of a Go Fund Me page to assist Christina's family.

"Words cannot begin to describe the pain I am feeling," Brian wrote. "I learned this business through the eyes of a father and Christina was like a second daughter to me.

"All I wanted to do was assist her in achieving her musical dreams while protecting her from the pitfalls associated with the business. I never could have imagined this horrific event being one of the pitfalls needing to be avoided."

In closing, he added, "Grimms I love you, and miss you beyond comprehension."